1. Field of the Invention
This invention relates to data conversion. The invention is especially directed to analog to digital (ADC) and digital to analog convertors (DAC). The invention is particularly directed to sigma delta (.SIGMA..DELTA.) modulators in data conversion and data converters of the foregoing kind.
Sigma delta (.SIGMA..DELTA.) modulators are well established for use in high resolution analog to digital and digital to analog data conversion. Their speed of operation, which is moderate by the standards of present-day data converters, is limited by the maximum achievable rate of clocking of the modulator's filters. Typically the filters in the sigma delta modulator must be clocked at 50 to 200 times the bandwidth of the signal to be converted.
2. Description of the Prior Art
A sigma delta modulator is comprised of an input sampler, a filter, a quantiser, and a feedback path to take the quantiser's output back to a summer at the input end of the filter. The quantiser output signal is also the modulator's output signal. The modulator is a clocked system. It may use either analog or digital signal processing. To simplify the explanation below, only analog signal processing sigma delta modulators are discussed.